Fig. 
Fig. 
Fig. 
Fig. 
Fig. 
ORTMANN: A MONOGRAPH OF THE NAJADES OF PENNSYLVANIA 343 
lla. Left inner gill. 116. Left outer gill. 
12. Quadrula undulata (Barnes) Male. Mahoning River, Mahoningtown, Lawrence 
County, Sept. 2, 1907. Cat. No. 61.3067. Specimen 17. 
12a. Right inner gill. 126. Right outer gill. 
13. Quadrula undulata (Barnes) Female, sterile. Mahoning River, Mahoningtown, 
Lawrence County, Sept. 2, 1907. Cat. No. 61.3067. Specimen 195. 
13a. Left inner gill. 18b. Left outer gill. 
14. Quadrula undulata (Barnes) Female, gravid (eggs). Shenango River, Linesville, 
Crawford County, June 19, 1909. Cat. No. 61.4839. Specimen 16. 
14a. Right inner gill. 14b. Right outer gill. 
15. Pleurobema esopus (Green) Male. Allegheny River, Kelly, Armstrong County, 
Sept. 5, 1907. Cat. No. 61.3064. Specimen 194. 
15a. Left inner gill. 15b. Left outer gill. . 
16. Pleurobema cesopus (Green) Female, gravid (eggs). Allegheny River, Kelly, 
Armstrong County, June 22, 1909. Cat. No. 61.4833. Specimen 38. 
16a. Left inner gill. 16b. Left outer gill. 
